One day, Billy bear spotted an apple tree in the forest. He became very hungry, so his salivary glands began to produce saliva.

He grabbed an apple from the tree and took a bite. Chewing his food broke it down into small enough pieces to be used for digestion. It also mixed with his saliva.

The enzyme amylase, which is produced in the mouth, helped break down large starch molecules into smaller sugar molecules.

When Billy swallowed his food, his tongue and roof of his mouth pushed it to the pharynx. This structure causes the trachea to close off so that food enters the gastrointestinal (GI) tract.

The apple pieces then entered the esophagus, which carries food from the mouth to the stomach. In the sac-like stomach, upper muscle relaxes to allow food to enter, while lower muscles mix food with digestive juices.

Gastrin, a hormone that plays a role in digestion, stimulates the secretion of stomach acid. These acids break down food by turning it into a liquid or paste instead of a solid.

Billy's food then enters the small intestine, which breaks down starches, proteins, and carbohydrates using pancreatic and bile fluids. This location is known as the “work house” of digestion since it is where most nutrients are absorbed into the bloodstream.

There are many enzymes found in the small intestine.

Lactase helps to digest lactose, a sugar found in milk and other dairy products.

Lipase assists in the transportation and processing of dietary lipids.

Proteases digest dietary proteins to allow absorption of amino acids in the small intestine.

The remaining contents move to the large intestine, also known as the colon. This five to seven foot long muscular tube is responsible for processing bodily waste.

The next destination is the rectum- an eight inch chamber that receives stool from the colon and holds it until evacuation occurs through the anus.

There are other organs that assist digestion along the way. The liver- secretes bile acids to break down fats and processes nutrient-rich blood from the small intestine before entering the bloodstream

The hormone secretin helps release liver secretions.